When carbon black is added to rubber compositions, the properties of the rubber compositions are greatly affected by the physical properties of carbon black, including the specific surface area, structure, and surface properties. Thus, various carbon blacks with different properties are used depending on the required properties of the rubber composition, the environmental conditions under which the rubber composition is used, or the like (see Patent Literature 1, for example).
Tread rubbers, which contact the ground, are required to have excellent resistance to abrasion (abrasion resistance) during driving and also to exhibit low hysteresis loss upon deformation of the rubber during driving and, therefore, low heat build-up properties. Several methods have been investigated to achieve both abrasion resistance and low heat build-up properties as described above, such as a method in which a rubber composition is highly filled with carbon black or a method in which a carbon black with a high specific surface area (a small particle size) or a high structure is used. However, these uses of carbon blacks may result in insufficient low heat build-up properties although abrasion resistance is improved.
In order to improve abrasion resistance of tires by controlling properties other than the specific surface area and the structure of carbon black, a method of increasing the sharpness of the aggregate diameter distribution of carbon black has been proposed. However, a rubber composition containing such a carbon black may have deteriorated low heat build-up properties, and a tire with a tread formed from the rubber composition may have insufficient low heat build-up properties. Moreover, reducing the sharpness (increasing the broadness) of the aggregate diameter distribution can improve the low heat build-up properties of tires, but at the same time tends to lower the abrasion resistance. Thus, controlling only the aggregate diameter distribution of carbon black is also not an effective way to achieve both abrasion resistance and low heat build-up properties of tires.
As described above, abrasion resistance and low heat build-up properties have a trade-off relationship. Although developments have been made to achieve high levels of both properties, a carbon black imparting sufficient properties has not yet been found.